Surfaces under continual exposure to sea water, for example ships, buoys, drilling platforms, underwater pipelines, fishing nets, etc., are under appropriate conditions colonized within a short time by marine organisms such as algae, seaweed, bivalves, tape worms, sponges, etc. This infestation is extremely disruptive in a large number of cases and is restrictive and a hindrance to the service properties of numerous facilities. For example, colonization of underwater ship areas leads to a restriction on the maneuverablilty of the ships and, because of the increased frictional resistance in the water, to a marked increase in fuel consumption.
For these reasons, infestation-preventing coating materials, known as antifouling paints, are employed widely for protecting underwater areas against colonization. These coating materials consist in most cases of a biocidal or nonbiocidal polymer and film-forming binder, co-biocides and pigments.
Frequently employed antifouling paints of recent years possess not only infestation-preventing but also self-polishing polymer film properties. In these systems the self-polishing effect is achieved by controlled hydrolysis of functional groups, leaving the surface of the coating hydrophilic and therefore erodible; coatings of this kind are described, for example, in EP-A-O 289 481. Antifouling paints which have found particularly broad use are those whose copolymers include triorganotin esters, especially tri-n-butyltin esters, of unsaturated carboxylic acids, for example (meth)acrylic acid. Examples of these are given in GB-A-1 457 590. Owing to the slow hydrolysis of the triorganotin ester group, these systems possess self-polishing properties coupled, through the biocidal action of the organotin compound, with outstanding antifouling properties. This particularly favorable combination of properties has led to widespread use of tin-based antifouling paints.
In years gone by there has been discussion about the use of tributyltin-and triphenyltin-containing coating compositions, since the rates of release of the organotin compounds into the sea water that have been customary to date do not appear to be necessary in all regions. Thus in some countries the release rate of tin-containing antifouling paints has been restricted to 4 .mu.g cm.sup.-2 d.sup.-1 TBT (tributyltin) and they can only be used on ships with a length of more than 25 m. There is therefore a need for effective, slowly hydrolyzable antifouling paint systems which are of reduced tin content and yet have adequate self-polishing properties.
The literature describes various examples of tin-containing antifouling paints which in addition to an organotin-containing monomer also include various other functionalized monomers. Thus EP 0 342 493 cites copolymers of tributyltin methacrylate, acrylamide and acrylic acid. Other systems are described in EP 0 200 433 (copolymers of tributyltin methacrylate, methyl methacrylate, styrene, ethylene glycol dimethacrylate and acrylonitrile), AU 466 764 (copolymers of tributyltin acrylate and vinyl acetate) and DD 279 258 (copolymers of tributyltin acrylate, methyl methacrylate and polyethylene glycol monoacrylate). However, all of these systems have either found no widespread commercial use or do not have the particularly favorable combination of infestation-preventing and self-polishing properties.
Furthermore, various examples of antifouling paints are mentioned which have groups which are hydrolyzable in sea water. For example, WO 84/02915 cites a large number of possible groups which should, with groups containing carboxylic acids, form readily hydrolyzable compounds. EP 0 204 444. EP 0 331 147 and GB 2 152 947 also describe ester-containing polymer systems for the antifouling sector. All of these systems, however, either have found no widespread commercial use or require a relatively complex multistage synthesis process for their preparation.